1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to a variety of relatively sliding portions in machine tools and testing equipment and in which a slider is mounted slidable on a track rail with rolling elements interposed therebetween.
2. Description of the Prior Art
In conventional linear motion rolling guide units, the sealing between a track rail and a slider that slides on it is realized by end seals attached to the ends of the slider and by under seals attached to the underside of the slider.
A linear motion rolling guide unit as shown in FIG. 6 is known. FIG. 6 shows a perspective view of one example of a conventional linear motion rolling guide unit.
As shown in the FIG. 6, the linear motion rolling guide unit includes a track rail 1 having raceway grooves 7 extending longitudinally on both side wall surfaces 5 thereof, and a slider 26 slidably mounted astride on the track rail 1. The slider 26 includes a casing 2, which has raceway grooves 6 formed at positions facing the raceway grooves 7 on the track rail 1, end caps 31 attached to the longitudinal ends of the casing 2, rolling elements 8 trapped and running between the opposing raceway grooves 6 and 7, retainer bands for keeping the rolling elements 8 from coming off the raceway grooves, and under seals 3 having seal portions. The end cap 31 has an end seal 25 for sealing between the track rail 1 and the slider 26. The end cap 31 is also provided with a grease nipple 24 for supplying lubricant to the sliding surfaces between the track rail 1 and the slider 26. To prevent the rolling elements 8 from coming off the casing 2, the retainer bands are provided to the casing 2 in such a way as to enclose the rolling elements 8. The under seals 3 are arranged at the underside of the slider 26 to seal between the casing 2 and the longitudinally extending sidewall surfaces 5 of the track rail 1 and to seal the undersides of the casing 2 and the end caps 31.
The slider 26 is mounted astride on the track rail 1 and freely slides on it by means of the rolling elements 8 that circulate along the raceways formed between the raceway grooves 7 on the track rail 1 and the raceway grooves 6 on the casing 2. The rolling elements 8 that travel loaded along the raceway grooves 7 of the track rail 1 are led to direction changing passages formed in the end caps 31 and further to return passages 27 formed in the upper part of the casing 2 parallel to the raceway grooves 6. Thus, the rolling elements 8 run endlessly through circulating passages. In this way, the slider 26 is allowed to slide relative to the track rail 1 by the rolling elements 8 traveling loaded between the raceway grooves 6 on the casing 2 and the raceway grooves 7 on the track rail 1.
The under seal 3 is mounted to the casing 2 by rivets and thus is difficult to mount or dismount. The under seal 3, though it has an advantage of being simple in construction and easily manufactured, also has drawbacks that because the under seal 3 is thin, it is easily deformed by external forces and by positioning errors between it and the casing 2 and track rail 1, the casing and track rail having the raceway grooves 6, 7 respectively.
In a dust prevention structure of a linear motion bearing apparatus disclosed in the Japanese Utility Model Laid-Open No. 98321/1991, the under seal is bent inwardly at both axial ends to make it U-shaped and is provided at the bent surfaces with inwardly protruding engagement projections, and the end caps are formed at their outer surfaces with recesses for receiving the engagement projections.
In an under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 118317/1991, axial ends of the under seal are formed with axially extending projections and end seals are formed at their lower end surfaces with engagement holes for receiving the projections of the under seal. Fitting the under seal into the end seals that have high strength makes the mounting and dismounting of the under seal easy and at the same time increases the strength of the under seal.
In another under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 121220/1991, the axial ends of the under seal are provided with two-pronged projections protruding toward the underside of the slider, the two prongs being elastically deformable toward and away from each other. The slider has the axial end portions of the underside thereof formed with vertical holes, into which the two-pronged projections of the under seal are fitted, and also with through-holes that intersect the vertical holes perpendicularly and pass through the arm or wing portions of the slides. One of the two prongs fitted into the vertical holes is elastically deformed in the vertical holes, thereby urging the under seal toward the side wall of a guide rail to bring the edge of the under seal into sliding contact with the guide rail.
The above under seal apparatuses for the linear motion guide bearings mount the under seal by fitting the projections or prongs of the under seal into the engagement holes in the slider or end seals.
The conventional linear motion rolling guide units generally have the construction in which the longitudinal ends of the under seal are fitted into the engagement holes in the end caps or end seals to mount the under seal to the end seals and in which the dust sealing member and the slider are made of different materials with different thermal expansions. Because of this, when the thermal expansion of the dust sealing member becomes larger than that of the slider, the dust sealing member will be deflected creating a gap between it and the guide rail or the underside of the casing, with the result that the sealing performance deteriorates, unable to prevent ingress of dust. That is, there must be some play for the under seal to move relative to the undersides of the casing and end caps so that the longitudinal elongation of the under seal due to thermal expansion difference between these parts can be offset by the engagement holes in the end caps or end seals. Otherwise, the under seal would be deformed as by buckling, degrading the sealing performance.
The conventional linear motion rolling guide unit, however, has the construction in which the projections of the under seal are engaged in the engagement holes in the end caps or end seals in such a way that they cannot move in the longitudinal direction. Further, since the under seal adheres to the undersides of the casing and end caps, the under seal cannot move causing deformations to the under seal and degrading the sealing performance. Furthermore, the conventional linear motion rolling guide unit, though it may facilitate the mounting and dismounting of the under seal, may not necessarily be able to position the under seal correctly and also has a problem that the under seal will be deformed by temperature variations and by swelling due to exposure to lubricants, deteriorating the sealing performance.